In order to meet the safety regulations imposed on facilities associated with the storage, use or disposition of radioactive materials used in nuclear reactors, or the monitoring of an accident situation, there is a critical requirement for a radiation monitoring apparatus which is both rugged and reliable, and capable of indicating fields from 1 R/hr up to 10.sup.8 R/hr and continue to operate even if exposed to high radiation doses and/or temperatures of up to approximately 250.degree. C.
Such an apparatus would find wide-spread use for monitoring radiation fields present at various locations around a nuclear power plant as well as monitoring radiation fields in stored fuel areas, high-level waste areas, as well as monitoring the activity in the primary coolant of a nuclear reactor.